Japanese Laid-Open Patent Publication No. 2005-192384 describes an example of a brushless motor that is an outer rotor type motor including a surface permanent motor (SPM) rotor and a Lundell-type stator. The SPM rotor includes a rotor core and permanent magnets attached to the surface of the rotor core. The Lundell-type stator includes two stator core bases and windings arranged between the stator core bases. Each stator core base includes claw poles arranged at equal intervals in the circumferential direction. In such a brushless motor, two types of windings are stacked in the axial direction. Power from a first system and power from a second system are applied to the two types of windings, respectively.
The brushless motor is a two-phase motor in which the Lundell-type stator is configured by a two-layer structure including winding for the first system and winding for the second system. However, a two-phase motor includes a dead point that adversely affects the starting characteristics of the motor.
A multi-Lundell-type motor includes a Lundell-type rotor and a Lundell-type stator. The Lundell-type rotor includes two rotor cores and a field magnet arranged between the rotor cores. Each rotor core includes claw poles arranged in the circumferential direction. The Lundell-type stator includes two stator cores and windings arranged between the stator cores. Each stator core includes claw poles arranged in the circumferential direction. The problem described above also occurs when the multi-Lundell-type motor has a two-layer two-phase tandem arrangement.
In the two-layer two-phase multi-Lundell-type motor, leakage magnetic flux from gaps between adjacent claw poles may lower the effective magnetic flux. In this case, high torque cannot be obtained with the motor.